The most common and most likely answer to this crossword clue is the 9 letter word THROWBACK
I've seen this crossword clue in The Daily Telegraph
T
H
R
O
W
B
A
C
K
Buddy explains!
The straight part
We know that "a reminder of the old days?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a reminder of the old days? = throwback.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THROWBACK mean?
THROWBACK noun- A reversion to an earlier stage of development.
- A person considered to be primitive, uncivilized and mentally deficient.
- An organism that has characteristics of a more primitive form.
- An atavism.
- A person similar to an ancestor, or something new similar to what already existed.